Pump assembly and method

ABSTRACT

A pump assembly comprises a centrifugal pump configured to pump a multiphase fluid, a suction conduit in fluid communication with the centrifugal pump, and a discharge conduit in fluid communication with the centrifugal pump. The pump further comprises an eductor comprising one or more motive nozzles disposed within the suction conduit. Wherein the one or more motive nozzles are configured to introduce a motive fluid into the suction conduit and toward the centrifugal pump along a suction direction roughly co-directional with the suction conduit toward the centrifugal pump. A method and a pump assembly for pumping a multiphase fluid are also presented.

BACKGROUND

This invention relates generally to pump assemblies and methods for pumping fluids. More particularly, this invention relates to pump assemblies employing centrifugal pumps and methods for pumping multiphase fluids.

Multiphase fluids, such as gaseous and liquid two-phase fluids exist in many areas of technology, such as oil production. Centrifugal pumps are often preferred when pumping multiphase process fluids, due to their lower cost, smaller size, and simplicity of operation and construction relative to other types of pumps, for example twin screw pumps.

One drawback to the use of centrifugal pumps in the operations involving multiphase process fluids, for example petroleum-gas mixtures from a subsurface reservoir, is the unintended segregation of the multiphase process fluid into its liquid and gaseous components as a result of shear forces applied to the multiphase process fluid by the rotating impellers of the centrifugal pump. In some instances, a liquid phase separates from the multiphase process fluid and moves to the periphery of the pump impellers while the gaseous components of the multiphase process fluid accumulate near the eyes of the impellers. As a result, the performance of the centrifugal pump may decrease and eventually it may no longer be possible to pump the multiphase process fluid effectively. This behavior may become particularly acute for multiphase process fluids characterized by a high gas volume fraction.

Therefore, there is a need for new and improved pump assemblies employing centrifugal pumps and methods for pumping multiphase fluids.

BRIEF DESCRIPTION

A pump assembly for pumping a multiphase fluid is provided in accordance with one embodiment of the invention. The pump assembly comprises a centrifugal pump configured to pump a multiphase fluid, a suction conduit in fluid communication with the centrifugal pump, and a discharge conduit in fluid communication with the centrifugal pump. The pump further comprises an eductor comprising one or more motive nozzles disposed within the suction conduit. Wherein the one or more motive nozzle are configured to introduce a motive fluid into the suction conduit and toward the centrifugal pump along a suction direction roughly co-directional with the suction conduit toward the centrifugal pump.

A method for pumping a multiphase fluid is provided in accordance with another embodiment of the invention. The method comprises introducing a multiphase fluid into a centrifugal pump via a suction conduit, receiving a discharge fluid from the centrifugal pump via a discharge conduit, and introducing a motive fluid into the multiphase fluid such that from initial contact of the multiphase fluid and the motive fluid, both fluids move unidirectionally along a flow path leading to the centrifugal pump.

Another aspect of the invention further provides a pump assembly for pumping a multiphase fluid. The pump assembly comprises a plurality of centrifugal pumps configured to pump a multiphase fluid, a suction conduit in fluid communication with the plurality of the centrifugal pumps, and a discharge conduit in fluid communication with the plurality of the centrifugal pumps. The pump assembly further comprises an eductor comprising one or more motive nozzles. The one or more motive nozzles are disposed within the suction conduit and configured to extend along a suction direction of the multiphase fluid so as to introduce a motive fluid into the suction conduit and toward the centrifugal pump.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features, and advantages of the present disclosure will become more apparent in light of the subsequent detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a pump assembly in accordance with one embodiment of the invention;

FIGS. 2-4 are schematic diagrams of arrangements of an eductor and an suction conduit of the pump assembly shown in FIG. 1 in accordance with various embodiment of the invention;

FIG. 5 is a schematic diagram of the arrangement of an eductor and an suction conduit of a pump assembly in accordance with an embodiment of the invention; and

FIG. 6 shows experimental data obtained using a pump assembly like that shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present disclosure are described herein with reference to the accompanying drawings. In the subsequent description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail.

FIG. 1 illustrates a schematic diagram of a pump assembly 10 for pumping a multiphase fluid 11 in accordance with one embodiment of the invention. The multiphase fluid 11 comprises two or more phases. In one embodiment, the multiphase fluid is a two phase fluid comprising a gaseous fluid and a liquid fluid. In an alternate embodiment, the multiphase fluid comprises at least three phases; for example a gaseous phase, a liquid phase and a solid phase. Examples of multiphase fluids include production streams from oil wells, process fluids in chemical manufacturing, and the like. In certain embodiments, the multiphase fluid may be a gas-liquid two-phase fluid and may include one or more of bubble, slug, transitional and mist flow type phases.

As illustrated in FIG. 1, the pump assembly 10 comprises a centrifugal pump 12, a suction conduit 13, a discharge conduit 14, a recirculation apparatus 15, and an eductor 16. In FIGS. 1-5 the same element numbers are used for the same or similar components unless specified otherwise.

It should be noted that the arrangements in FIG. 1 is merely illustrative. In some applications, the pump assembly 10 may comprise a plurality of centrifugal pumps 12 configured in parallel or in serials. In various embodiments, each of the centrifugal pumps 12 may be a radial flow pump, an axial flow pump, or a mixed-flow type pump and may be configured for single stage or multistage operation. The suction conduit 13 may be in fluid communication with a multiphase fluid source (not shown) and configured to deliver the multiphase fluid 11 from the multiphase fluid source into the centrifugal pump 12. The action of the centrifugal pump 12 on the multiphase fluid 11 results in the formation of a discharge fluid (not shown), which may be removed via discharge conduit 14.

In some applications, the discharge fluid may also be multiphase and have a higher or same total pressure than that of the multiphase fluid. In non-limiting examples, the discharge fluid may be discharged from any stage of the centrifugal pump when the centrifugal pump has a multistage configuration. Additionally, since the multiphase fluid 11 passes through the centrifugal pump 12, the discharge fluid may have a lower gas volume fraction (GVF) than that of the multiphase fluid.

For certain arrangements, the suction conduit 13 and/or the discharge conduit 14 may be detachably assembled onto the centrifugal pump 12 for delivering the multiphase fluid into and the discharge fluid away from the centrifugal pump 12, respectively. In other applications, the suction conduit 13 and/or the discharge conduit 14 may be unitary with the centrifugal pump 12, for example, to function as a suction nozzle 24 (shown in FIG. 3) and a discharge nozzle (not shown) of the centrifugal pump 12, respectively. For such a configuration, in some examples, one or more additional conduits may be employed to deliver the multiphase fluid into the centrifugal pump 12 via the suction conduit (suction nozzle) 13 and/or deliver the discharge fluid away from the centrifugal pump 12 via the discharge conduit (discharge nozzle) 14. In some examples, the term “unitary” indicate more than one element may be integrated together by some known methods, such as molding, welding and riveting, and may function as one element.

In the example illustrated in FIG. 1, the recirculation apparatus 15 is disposed downstream from the centrifugal pump 12 and in fluid communication with the discharge conduit 14 for receiving the discharge fluid from the centrifugal pump 12. The eductor 16 is in fluid communication with a lower portion of the recirculation apparatus 15 via a connection conduit 20.

In non-limiting examples, the recirculation apparatus 15 may comprise a container 17 and a separator (not shown) disposed within the container 17 for gas and liquid separation of the discharge fluid. Non-limiting examples of the separator include a cyclone separator and a static separator with enhanced gravity. In some applications, the separator may not be employed and the discharge fluid may be separated by gravity separation.

Thus, when the discharge fluid is delivered into the container 17, the separator performs the gas and liquid separation of at least a portion of the discharge fluid in the container 17, so that a motive fluid 22 (shown in FIG. 2) may accumulate at the lower portion of the container 17 for delivery into the eductor 16 while a fluid accumulated at an upper portion of the container 17 may be discharged out of the recirculation apparatus with/without other portions of the discharge fluid for certain applications via a conduit 19.

In some examples, due to the higher total pressure of the discharge fluid and the presence of the separator, the motive fluid may also have a higher total pressure and a lower GVF than those of the multiphase fluid. Additionally, in some applications, since the discharge fluid may have a lower GVF than that of the suction fluid 11, the separator may not be employed and at least a portion of the discharge fluid may act as the motive fluid to pass through the container 17 for delivery into the eductor 16.

In the illustrated example in FIG. 1, the recirculation apparatus 15 is connected to one end of the discharge conduit 14, so that all of the discharge fluid from the discharge conduit may pass through the recirculation apparatus 15 for discharging and/or processing, such as the gas and liquid separation. Alternatively, only a portion of the discharge fluid may pass through the recirculation apparatus 15. For example, the recirculation apparatus 15 is disposed to bypass the discharge conduit 14 to receive a portion of the discharge fluid. Thus, in certain applications, the container 17 may not be employed.

The eductor 16 is assembled onto the suction conduit 13 and is configured to receive and eject the motive fluid from the recirculation apparatus 15 into the suction conduit 13 to improve flow conditions of the suction fluid, for example reducing the GVF of the multiphase fluid. In some applications, the eductor 16 may be detachable disposed on or be unitary with the suction conduit 13.

FIG. 2 illustrates a schematic diagram of an arrangement of the eductor 16 and the suction conduit 13 of the pump assembly 10 in accordance with one embodiment of the invention. As illustrated in FIG. 2, the eductor 16 comprises a motive pipe 20 and a motive nozzle 21 disposed at one end of the motive body 20. The motive nozzle 21 has a taper shape and the suction conduit 13 has a cylindrical shape. Alternatively, the motive nozzle 21 and the suction conduit 13 may have other shapes, for example, the motive nozzle 21 has a cylindrical shape.

For the arrangement illustrated in FIG. 2, the motive pipe 20 is in fluid communication with the recirculation apparatus 15 with the other end thereof via the connection conduit 18 (shown in FIG. 1) for delivering the motive fluid from the recirculation apparatus 15 into the motive nozzle 21. The motive nozzle 21 is accommodated into and configured to reject the motive fluid into the suction conduit 13 to mix with the multiphase fluid 11. In some examples, the motive nozzle 21 may be detachably disposed on or be unitary with the motive pipe 20.

In some applications, the motive nozzle 21 may introduce the motive fluid into the suction conduit 13 and toward the centrifugal pump 12 along a suction direction 23 or a flow direction roughly co-directional with the flow of the multiphase fluid through the suction conduit 13 toward the centrifugal pump 12, which may indicate that, in some examples, the motive nozzle 21 may extend along an axis (not shown) parallel to an axis of the suction conduit 13, as depicted in FIG. 2. In other examples, as depicted in FIG. 3, each of the two motive nozzles 21 extends along an axis having an acute angle with the axis of the suction conduit 13 to introduce the motive fluid into the suction conduit 13 and toward the centrifugal pump 12 along a suction direction.

Thus, the motive fluid is introduced into the multiphase fluid such that from initial contact of the multiphase fluid and the motive fluid, both fluids move unidirectionally along a flow path leading to the centrifugal pump. In some example, the motive nozzle 21 may be coaxial with the suction conduit 13. In one example, the suction direction indicates a substantially horizontal flow direction.

It should be noted that the arrangements in FIGS. 2-3 are merely illustrative. For the arrangement in FIG. 2, in some applications, as illustrated in FIG. 4, more than one motive nozzle 21 may be disposed along the axis parallel to the axis of the suction conduit 13 to introduce the motive fluid into the suction conduit 13. For the arrangement in FIG. 3, in certain applications, one or more than two motive nozzles 21 may be disposed along the axis having an acute angle with the axis of the suction conduit 13 to introduce the motive fluid into the suction conduit 13. In non-limiting examples, the pump assembly 10 may comprise the arrangements of the motive nozzles shown both in FIGS. 2 and 3 simultaneously.

For some arrangements, the motive fluid may have a higher total pressure and a lower GVF than those of the multiphase fluid 11. Thus, during the motive fluid is ejected into the suction conduit 13 and mixes with the multiphase fluid 11, a static pressure and a flow velocity of a mixture fluid, which may also act as a suction fluid, of the motive fluid and the multiphase fluid 11 are increased. Meanwhile, the increased pressure of the multiphase fluid and compressibility of the gaseous liquids therein result in that the multiphase fluid may have a lower GVF for suction into the centrifugal pump 12.

Accordingly, in non-limiting examples, the mixture fluid may have a higher pressure and a lower GVF due to the higher pressure of the motive fluid, so that the flow conditions of the mixture fluid may be enhanced to ensure stable operation of the centrifugal pump 12 without loss of prime even though the multiphase fluid 11 has a higher GVF before suction into the centrifugal pump 12.

FIG. 5 illustrated a schematic diagram of the arrangement of the eductor 16 and the suction conduit 13 in accordance with another embodiment of the invention. The arrangements in FIGS. 2 and 5 are similar, and the two arrangements differ in that the motive nozzle 21 shown in FIG. 2 is disposed within the suction conduit 13. The motive nozzle 21 shown in FIG. 5 not only extends along the suction direction of the multiphase fluid, but also extends into the centrifugal pump 12, for example, one end of the motive nozzle 21 extends into the suction nozzle 24 of the centrifugal pump 12.

Additionally, for the arrangement illustrated in FIG. 1, the pump assembly 10 further comprises a detector 25 and a control valve 26 connected to the detector 25. The detector 25 is disposed between the eductor 16 and the centrifugal pump 12 for detecting the GVF of the multiphase fluid in the suction conduit 13. The control valve 26 is disposed between the eductor 16 and the recirculation apparatus 15 to control the flow of the motive fluid in the conduit 18. Non-limiting examples of the detector 25 include a multiphase flow meter or other suitable detectors based on pressures, temperatures and/or flow rates of the multiphase fluid for detecting GVF thereof.

Thus, during operation, the centrifugal pump 12 is actuated, for example using an electrical motor (not shown) to pump the multiphase fluid 11 via the suction conduit 13. The detector 25 detects the GVF of the multiphase fluid 11 while the multiphase fluid 11 enters into the centrifugal pump 12 and at least a portion of the discharge fluid enters into the recirculation apparatus 15. Then, when the GVF of the multiphase fluid 11 exceeds a threshold value, the detector 25 triggers the control valve 26 to open the conduit 18, so that the motive fluid is ejected into the suction conduit 13 to mix with the multiphase fluid 11 via the eductor 16 so as to decrease the GVF of the mixture fluid (suction fluid) to ensure stable operation of the centrifugal pump 12. Next, when the GVF of the mixture fluid drops below the threshold value, the detector 25 triggers the control valve 26 to close the conduit 18 and conserve the motive fluid in the recirculation apparatus 15.

In some examples, the detector 25 may not be employed. For example, before delivery of the motive fluid into the suction conduit 13, when the GVF of the multiphase fluid 11 exceeds the threshold value, the centrifugal pump 12 may vibrate due to the accumulation of the gaseous fluid and imbalance flow in the pump 12. Thus, one may turn on the control valve manually to make the motive fluid enters into the eductor 16 via the conduit 25.

It should be noted that the arrangements in FIGS. 1-5 are merely illustrative. For some arrangements, the recirculation apparatus 15 may not be employed. As mentioned above, in some examples, the discharge fluid may function as the motive fluid. Thus, the eductor 16 may be directly in fluid communication with the discharge conduit 14 and receive at least a portion of the discharge fluid from the discharge conduit 14 for injection into the suction conduit 13.

For other arrangements, a motive fluid source (not shown) separated from the discharge conduit 14 may be provided to be in fluid communication with and provide a motive fluid with a higher pressure to the eductor 16. In certain applications, the motive fluid from the separated fluid source may have a lower GVF than that of the multiphase fluid 11. Alternatively, the motive fluid may have the same GVF as or a higher GVF than that of the multiphase fluid 11.

FIG. 6 shows example experimental data obtained using the pump assembly 10 shown in FIG. 1. As illustrated in FIG. 6, with regarding to respective GVF of the multiphase fluid 11, the pump assembly 10 with the eductor has a higher discharge pressure than that a pump assembly without the eductor, which indicates the accumulation of the gaseous fluid and the flow imbalance of the multiphase fluid is reduced in the pump assembly with the eductor, so that the pump assembly with the eductor has a stable performance and higher efficiency.

While the disclosure has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the disclosure herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to fall within the spirit and scope of the disclosure as defined by the claims presented herein. 

1. A pump assembly for pumping a multiphase fluid, the pump assembly comprising: a centrifugal pump configured to pump a multiphase fluid; a suction conduit in fluid communication with the centrifugal pump; a discharge conduit in fluid communication with the centrifugal pump; and an eductor comprising one or more motive nozzles disposed within the suction conduit; wherein the one or more motive nozzles are configured to introduce a motive fluid into the suction conduit and toward the centrifugal pump along a suction direction roughly co-directional with the suction conduit toward the centrifugal pump.
 2. The pump assembly of claim 1, wherein at least one of the one or more motive nozzles is disposed along an axis parallel to an axis of the suction conduit.
 3. The pump assembly of claim 1, wherein at least one of the one or more motive nozzles is coaxial with the suction conduit.
 4. The pump assembly of claim 1, wherein the eductor is in fluid communication with the discharge conduit and is configured to receive at least a portion of a discharge fluid.
 5. The pump assembly of claim 4, wherein the centrifugal pump is a multistage centrifugal pump.
 6. The pump assembly of claim 4, further comprising a recirculation apparatus disposed between the discharge conduit and the eductor, the recirculation apparatus being configured to deliver the at least a portion of the discharge fluid into the eductor.
 7. The pump assembly of claim 4, further comprising a control valve disposed between the eductor and the discharge conduit.
 8. The pump assembly of claim 4, further comprising a detector for detecting a gas volume fraction of one or more of the multiphase fluid, and a mixture fluid of the motive fluid and the multiphase fluid.
 9. A method for pumping a multiphase fluid, the method comprising: introducing a multiphase fluid into a centrifugal pump via a suction conduit; receiving a discharge fluid from the centrifugal pump via a discharge conduit; and introducing a motive fluid into the multiphase fluid such that from initial contact of the multiphase fluid and the motive fluid, both fluids move unidirectionally along a flow path leading to the centrifugal pump.
 10. The method of claim 9, wherein the motive fluid being introduced has a total pressure at least equal the total pressure of the multiphase fluid in the suction conduit.
 11. The method of claim 9, wherein the motive fluid has a lower gas volume fraction than that of the multiphase fluid.
 12. The method of claim 9, wherein the motive fluid is introduced into the multiphase fluid via one or more motive nozzles.
 13. The method of claim 12, wherein at least a portion of the discharge fluid is used as the motive fluid.
 14. The method claim 13, further comprising directing a portion of the discharge fluid to a recirculation apparatus in fluid communication with the one or more of the motive nozzles via a conduit.
 15. The method of claim 9, further comprising detecting a gas volume fraction of one or more of the multiphase fluid, and a mixture fluid of the motive fluid and the multiphase fluid in the suction conduit.
 16. The method of claim 15, wherein said detecting triggers a control valve to regulate the introduction of motive fluid into the multiphase fluid.
 17. A pump assembly for pumping a multiphase fluid, the pump assembly comprising: a plurality of centrifugal pumps configured to pump a multiphase fluid; a suction conduit in fluid communication with the plurality of the centrifugal pumps; a discharge conduit in fluid communication with the plurality of the centrifugal pumps; and an eductor comprising one or more motive nozzles disposed within the suction conduit and configured to extend along a suction direction of the multiphase fluid so as to introduce a motive fluid into the suction conduit and toward the plurality of the centrifugal pumps.
 18. The pump assembly of claim 17, wherein at least one of the one or more motive nozzles is disposed along an axis parallel to an axis of the suction conduit.
 19. The pump assembly of claim 17, wherein at least one of the one or more motive nozzles is disposed along an axis having an acute angle with an axis of the suction conduit.
 20. The pump assembly of claim 17, wherein the eductor is in fluid communication with the discharge conduit and is configured to receive at least a portion of a discharge fluid.
 21. The pump assembly of claim 17, wherein the plurality of centrifugal pumps are configured in parallel.
 22. The pump assembly of claim 17, wherein the plurality of centrifugal pumps are configured in series. 